Release 0.13.1

Update hotdoc_lumen_theme

To use the theme, pass to hotdoc:

--html-theme=https://github.com/hotdoc/hotdoc_lumen_theme/releases/download/0.13.1/hotdoc_lumen_theme-0.13.1.tar.xz?sha256=f04c0808270cddd5436d445e28d7c67acf8e49f730181f1c6c13257c48849f5d

Hotdoc bootstrap theme commit:

commit 2cba7e7188527358effcc63524f246dbd575d1ed
scrollspy: initialize from javascript on document.ready